The present invention relates to an automatic sewing machine, in which a relative movement between a workpiece and a sewing head is controlled by a computer receiving a program according to a predetermined contour to be stitched. In particular, this invention relates to a method and a device for protecting an automatic sewing machine of the aforesaid character from damage from collision between the sewing head and the workpiece clamp.
In such CNC-controlled sewing machines an individual sewing contour is given by a program stored on a data carrier, e.g. a punched tape or an EPROM-cassette into the computer. The contour represents the path of the needle with respect to the workpiece. The contour is determined by perpendicular coordinates of some significant points, which form the variables of an algorithm applied for figuring all required values of a contour by using linear or square interpolation. Thus, by the input of such significant points the basic profile of the contour is determined. Furthermore, it is required that the workpiece clamp is formed with a profile that is matched to the contour controlled by the computer. In case of an implementation of a workpiece clamp that does not fit to the programmed contour, the sewing head of the sewing machine or the workpiece clamp and under particular circumstances the drive motors will be damaged. Therefore, it is necessary to check the matching of an inserted workpiece clamp with the computer-controlled contour prior to initiating a sewing process. Since this checking procedure should be performed in a minimum of time on one hand and mis-operation on the other hand must be eliminated, it has proved necessary to automatically perform this control procedure prior to the sewing process, and to carry out the control without any action from the operator.
In a known automatic sewing machine there are four microswitches which cooperate with exchangeably contoured workpiece clamps. After the installation of a certain workpiece clamp, a characterizing shift status is indicated by the switches which are being read and compared by the computer with the loaded program. Only after this checking procedure can the sewing process be initiated as far as both, the loaded program and the workpiece clamp show an associated contour. Indeed, with this known application of a number of switches for identifying a workpiece clamp, a damaging of the automatic sewing machine caused by mis-operation is eliminated. However, it is necessary to install a plurality of switches including wiring, which is costly. Due to the physical extension of such switches the number of identification codes is limited to the number of sixteen, with four switches.
Another shortcoming in the operation of such sewing machines is known from the fact that the actual sewing contour may deviate from the theoretically programmed contour. Such uncontrolled deviations which itself may be of minor extent can, by accumulation, also lead to a collision between the sewing head and the workpiece clamp.
Accordingly, the main object of the present invention is to provide a method to prevent the expensive item of equipment such as an automatic sewing machine from damage from collision of the sewing head and the workpiece clamp. Therefore, a method is provided for safe operation of an automatic sewing machine to automatically carry out a checking procedure with respect to the contour of the workpiece clamp and the contour controlled by the computer by using already existing components of the computer.
Another object of the present invention is to carry out the foregoing method so that the movably arranged sewing head is moved out of the way for making possible the exchange of the workpiece clamp.
Still a further object of this invention is to provide a device of simple construction for carrying out the aforesaid method in which contoured workpiece clamps include low-cost rigid code elements for identification.
Still a further object of the present invention is to provide a device for carrying out the aforesaid method in which the number of identification codes for differently contoured workpiece clamps is inexpensively increased.
Still another object of this invention is to provide a device of the aforesaid type which is reliable in operation.
A further object of this invention is to include an alignment procedure in the afore-described method, in which errors arising during the operation of the machine are automatically corrected.